Ch, XVI.] EOCENE STRATA. 231 



Dr. T. Thomson found nummulites at an elevation of no less than 

 16,500 feet above the level of the sea, in Western Thibet. 



One of the species, which I myself found very abundant on the flanks 

 of the Pyrenees, in a compact crystalline marble 

 (%. 242) is called by M. D'Archiac Nummulites 

 Piischi. The same is also very common in rocks of 

 the same age in the Carpathians. 



Another large species (see fig. 243), Nummulites 

 exponens, J. Sow., occurs not only in the South of 

 France, near Dax, but in Germany, Italy, Asia Minor, 

 and in Cutch ; also in the mountains of Sylhet, on the mimmuUteg ea^pone-as. 



frontiers of China, ^"^^- Europe and India. 



In many of the distant countries above alluded to, in Cutch, for exam- 

 ple, some of the same shells, such as Nerita conoidea (l.g. 240), accom- 

 pany the Nummulites as in France. 



The opinion of many observers, that the nummulitic formation belongs 

 partly to the cretaceous era, seems chiefly to have arisen from confound- 

 ing an alHed genus, Orbitoides, with the true Nummulite. 



When we have once arrived at the conviction that the nummulitic for- 

 mation occupies a middle place in the Eocene series, we are struck with 

 the comparatively modern date to which some of the greatest revolutions 

 in the physical geography of Europe, Asia, and Northern Afiica must be 

 referred. All the mountain chains, such as the Alps, Pyrenees, Carpa- 

 thians, and Himalayas, into the composition of whose central and loftiest 

 parts the nummulitic strata enter bodily, could have had no existence till 

 after the Middle Eocene period. During that period the sea prevailed 

 where these chains now rise, for nummulites and their accompanying tes- 

 tacea were unquestioijfebly inhabitants of salt water. Before these events, 

 comprising the conversion of a wide area from a sea to a continent, Eng- 

 land had been peopled, as I before pointed out (p. 219), by various 

 quadrupeds, by herbivorous pachyderms, by insectivorous bats, by opos- 

 sums and monkeys. 



Almost all the extinct volcanoes which preserve any remains of their 

 original form, or from the craters of which lava streams can be traced, 

 are more modern than the Eocene fauna now under consideration ; and 

 besides these superficial monuments of the action of heat, Plutonic influ- 

 ences have worked vast changes in the texture of rocks within the same 

 period. Some members of the nummulitic and overlying tertiary strata 

 called Jiysch have actually been converted in the Central Alps into crys- 

 talline rocks, and transformed into marble, quartz-rock, mica-schist, and 

 gneiss."^ 



EOCENE STRATA IN THE UNITED STATES. 



In North America the Eocene formations occupy a large area 

 bordering the Atlantic, which increases in breadth and imjwrtance as 

 it is traced southwards from Delaware and Maryland to Georgia and 



* Murchison, Quart. Journ. of Geol. Soc. vol. v., and Lyell, vol. vi. 1850, Anni. 

 versary Address. 



